I’m going to take a guess that this is related to your post here.
If you look at my response to that one, you’ll see I’m using the content of the draft in the append. You are using the draft. That could be one reason. My first recommendation would therefore be to try that.
Going further on the debugging if that does not work, I would use two quick look actions in the loop.
One quick look at the start to look at the content of the draft - so that you can see Shortcuts has picked up the draft content.
One quick look at the end to look at the content of the Evernote note (if you read the append to Evernote action in Shortcuts, you’ll see the result is the Evernote note, and when you add it to quick look, the default valuer as ‘Evernote Note’ is the content of the note).
Now you know what is being sent to Evernote and what is being stored/returned by Evernote.
Of course, as you noted, an alternative approach would be to collect all of the content from Drafts first, and then append it in one go to Evernote. That should also eliminate any timing glitches by only having a single access run against Evernote. It is just a reshuffling of what you had above, or in this case, what I posted on your other query, as it saved me some fiddling around, and you get the bonus of what would auto archive the processed drafts.
Hope that helps.